1. Field of the Invention
The present invention relates generally to controlling vehicles at least having an internal combustion engine mounted therein, and particularly to vehicular control devices reducing catalytic odor present in emissions cleaned by a catalyst and then emitted into the air.
2. Description of the Background Art
Emissions from an engine serving as a source driving a vehicle contain air pollutants including carbon monoxide (CO) generated when fuel incompletely combusts, hydrocarbon (HC) resulting from fuel failing to combust and having evaporated, and nitrogen oxide (NOx) bound to nitrogen and oxide present in the air internal to a combustion chamber having high temperature. These substances affect environment, and accordingly they must be removed before they are emitted into the air. This is addressed by providing an exhaust pipe at an intermediate portion with a catalytic converter. This catalytic converter employs platinum and rhodium or palladium and rhodium plus palladium as a catalyst. These elements react with the three types of air pollutants to provide carbon dioxide (CO2), water (H2O) and nitrogen (N2). As the catalytic converter causes the three types of chemical substances to react, it is also referred to as a three way catalyst.
If for such a catalytic converter 1) the catalyst has high temperature, 2) the vehicle is in a small load range having a small amount of exhaust gas (i.e., a small amount of air is taken in), and 3) an air fuel ratio having been controlled is rich on average, then the catalytic converter internally has a reducing atmosphere and catalytic odor is caused. More specifically, fuel contains sulfur (S), which is oxidized to be SOx which in turn adheres to the catalyst and when the above three conditions are satisfied the reducing atmosphere is provided and therein the absorbed SOx is reduced to generate a sulfuric odor (hydrogen sulfide (H2S)). More specifically, a catalytic odor attributed to a sulfuric compound contained in fuel is caused as hydrogen sulfide is generated by the following reaction:SO2+3H2→H2S+2H2O.More specifically, hydrogen sulfide is generated presumably because the fuel has a sulfuric component combusted and thus becoming sulfur dioxide gas, which in turn reacts with hydrogen generated during a combustion process.
Such catalytic odor attributed to the fact that the fuel has such a property (or contains a sulfuric component) is more significantly caused for richer average air fuel ratios, as has been described above. For leaner air fuel ratios, the following reaction:2SO2+O2→2SO36SO3+4CeO2→2Ce2(SO4)3+O2presumably provides a sulfur oxide which is in turn absorbed by the catalyst.
Furthermore for richer air fuel ratios oxygen exists in a small amount and such oxygen binds to hydrogen to generate H2O. However, as the oxygen exists in the small amount, hydrogen is excessively generated and binds to sulfur. This helps to generate H2S, which is also considered as an obstacle in reducing catalytic odor. For leaner air fuel ratios, oxygen exists in a large amount and such oxygen binds to hydrogen and thus helps to generate H2O. Hydrogen is less excessively generated and accordingly so is H2S, which presumably reduces catalytic odor.
In a point of view different from such catalytic (or bad) odor, the three way catalyst has a cleaning characteristic depending on an air fuel ratio of an air fuel mixture formed in a combustion chamber and when the air fuel ratio is close to a stoichiometric air fuel ratio the three way catalyst functions most effectively. This is because when an air fuel ratio is lean and exhaust gas has a large amount of oxygen, oxidation is enhanced in activity however reduction is reduced in activity, and when an air fuel ratio is rich and exhaust gas has a small amount of oxygen, reduction is enhanced in activity however oxidation is reduced in activity, and as a result the above mentioned three harmful components cannot all be cleaned satisfactorily. Accordingly, internal combustion engines having a three way catalyst have an exhaust manifold provided with a linear oxygen sensor measuring an oxygen concentration which is in turn used to feed back the combustion chamber's internal air fuel mixture to control it to achieve the stoichiometric air fuel ratio.
It is generally known that a three way catalyst is provided with a capability to store oxygen (or an oxygen storage) to prevent the three way catalyst from providing impaired emission cleaning performance if an air fuel mixture temporarily has a lean or rich air fuel ratio. Thus for the lean air fuel ratio excessive oxygen is stored and for the rich air fuel ratio the stored oxygen is used to maintain satisfactory emission cleaning performance.
More specifically, the three way catalyst has a function taking in and storing excessive oxygen present in exhaust gas for the lean air fuel ratio to reduce NOx. In contrast, when an air fuel ratio becomes rich, HC and CO filling to combust and thus present in exhaust gas deprive the three way converter of the oxygen stored therein and are thus oxidized. Accordingly, when an air fuel ratio deviates from the stoichiometric air fuel ratio and NOx is accordingly to be reduced the three way catalyst must be in a condition capable of storing oxygen (i.e., the three way catalyst must store oxygen in an amount that has a sufficient margin relative to a maximum oxygen occlusion), and in contrast, to oxidize uncombusted CH and CO the three way catalyst must store an amount of oxygen sufficient.
To be able to reduce NOx for an air fuel ratio deviating from the stoichiometric air fuel ratio to a lean air fuel ratio and oxidize uncombusted HC and CO for an air fuel ratio deviating from the stoichiometric air fuel ratio to a rich air fuel ratio the three way catalyst preferably has an oxygen occlusion maintained to correspond to approximately half a maximum oxygen occlusion.
There exists a well-known hybrid vehicle having mounted therein an internal combustion engine having a stop mode when the vehicle is running, and an electric motor. In such hybrid vehicle the engine is stopped depending on the vehicle's state of operation, a driving battery's state, and the like, and such states thereafter are also detected and the engine is restarted, as required, to enhance fuel economy. Thus the engine is intermittently operated (or stopped by interrupting (or cutting) the fuel supplied thereto) to achieve enhanced fuel economy. When the vehicle is operated and the engine stops, and an electronic control unit (ECU) determines that the engine stops, the fuel supplied to the engine is immediately interrupted (or cut). While the engine is prevented from receiving the fuel, the engine still has an inertial force and its crankshaft's rotation does not immediately stop. As the crankshaft rotates, intake and exhaust valves open and close and the engine accordingly takes in air, however the engine is not supplied with fuel and its emissions are lean. In that case, as the fuel is cut, the three way catalyst readily reaches its limit in oxygen occlusion, and cannot exhibit a desired catalytic cleaning performance when the engine is restarted.
Japanese Patent Laying-Open No. 2003-083121 discloses a catalytic emission cleaner for an internal combustion engine that can address such disadvantage utilize an emission cleaning catalyst's oxygen occlusion capability to provide further enhanced emission cleaning performance. As disclosed in the publication, the emission cleaner utilizes an oxygen occlusion effect of an emission cleaning catalyst arranged on an emission path of the internal combustion engine having an engine stop mode stopping the engine when the vehicle is operated. The emission cleaner includes a calculator calculating the catalyst's oxygen occlusion, and an air fuel ratio controller driven by the calculated oxygen occlusion to control the internal combustion engine's air fuel ratio. The calculator also calculates oxygen occlusion in the engine stop mode and air fuel ratio controller is driven by the oxygen occlusion calculated by the calculator in the engine stop mode to control an air fuel ratio after the mode is cleared when the engine restarts.
This catalytic emission cleaner allows oxygen occlusion to be also calculated in the engine stop mode and allows an air fuel ratio after the engine's restart to be controlled as based on oxygen occlusion capability. This can reduce the deterioration in emission cleaning performance that is provided immediately after the engine is restarted, and thus provided further enhanced emission cleaning performance. Herein controlling an air fuel ratio immediately after the engine's restart how the air fuel ratio varies within a predetermined period of time can be determined to prevent emission cleaning performance from significantly deteriorating immediately after the engine is restarted restart and thus provide further enhanced emission cleaning performance.
The above publication discloses that the three way catalyst's oxygen occlusion is controlled by modifying the engine's output and the motor's output in ratio, cutting the fuel helps oxygen occlusion to reach a limit, and that while the fuel is cut the motor must output all of torque required for the vehicle. The publication is, however, silent on catalytic odor. More specifically, if with the fuel cut the engine is restarted regardless of catalytic odor reduction control, the engine can emit rich exhaust gas, and as described above, in such rich condition a catalytic odor (H2S) can be generated disadvantageously.